Erfan wrote:

> hi, i am now learing linux Socket programn . when i read some
> codes,that the function bind and connect puzzled me. That is :
> int bind(int socket,const struct sockaddr *address,size_t
> address_len)
>
> my confusion focus on the sencond parameter,"const struct sockaddr
> *address". what does it mean?

It means that the parameter must be a pointer to a "struct sockaddr".

> I found it in a programn that is used as "bind(server_socked,(struct
> sockaddr *)&server_address,server_len)".
> what happen to (struct sockaddr *)&server_address?
> As far as i know,&& in C means "AND" or" *",what about "&"?

If you have a variable named "var", then "&var" returns the address
of "var". So, "&server_address" means "the address of variable
server_address". This address can be used anywhere a pointer to a
variable of that type is expected.

The variable "server_address" is not usually of type "struct sockaddr"
(but instead, for example, "struct sockaddr_in"), so the address obtained
with "&server_address" is the address (following the example) of a "struct
sockaddr_in". bind(), OTOH, expects as second parameter the address of a
plain "struct sockaddr", so the programmer must perform a cast to convert
the value into the expected type. That's what the (struct sockaddr *) does.

> My misunderstanding on function connect,i think,is the same as the
> function bind.

I suggest that you investigate C pointers and casts.

On Mon, 11 Feb 2008 06:29:59 -0800, Erfan wrote:

> hi, i am now learing linux Socket programn . when i read some
> codes,that the function bind and connect puzzled me. That is :
> int bind(int socket,const struct sockaddr *address,size_t
> address_len)
>
> my confusion focus on the sencond parameter,"const struct sockaddr
> *address". what does it mean?
> I found it in a programn that is used as "bind(server_socked,(struct
> sockaddr *)&server_address,server_len)".
> what happen to (struct sockaddr *)&server_address?
> As far as i know,&& in C means "AND" or" *",what about "&"?
> My misunderstanding on function connect,i think,is the same as the
> function bind.

This is actually a C question. &server takes the address of the variable
server. (struct sockaddr *) casts it to the appropriate type for this
function. If this is chinese to you, I suggest you try in a C oriented
group.

HTH,
M4